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ABSTRACT: A highly stereo-, regio-, and chemoselective method has been devised for the synthesis of a wide range of spirooxindolyl oxazolidines via an intermolecular 1,3-dipolar cycloaddition of carbonyl ylides generated from dimethyl diazomalonate and aromatic aldehydes, with cyclic ketimines using 5 mol % of Rh2(OAc)4 under mild conditions. Similarly, highly functionalized spirooxindolyl pyrrolines have also been prepared through 1,3-dipolar cycloaddition of azomethine ylides generated from dimethyl diazomalonate and cyclic ketimines, with dimethyl acetylenedicarboxylate.
Organic Letters 03/2013; · 5.86 Impact Factor
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ABSTRACT: A novel method has been devised for the synthesis of 2,4,5-trisubstituted pyrrole derivatives through the coupling of α-diazoketones with β-enaminoketones and esters using 10 mol % of Cu(OTf)(2). A wide range of 2,3-disubstituted indole derivatives were also prepared from α-diazoketones and 2-aminoaryl or alkyl ketones. The synthetic versatility of this approach has been exemplified in the formal synthesis of homofascaplysin C.
Organic Letters 01/2013; · 5.86 Impact Factor
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ABSTRACT: Novel synergistic effects between Lewis and Brønsted acids in Prins cyclization are reported. Non-reactive Lewis acids and non-reactive Brønsted acids, which failed to perform Prins cyclization when used alone, have shown remarkable synergistic effects when used in combination to perform the reaction successfully.
Chemical Communications 08/2012; 48(74):9316-8. · 6.17 Impact Factor
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ABSTRACT: A novel intramolecular Prins cyclization of (Z)-2-(5-hydroxypent-2-enyl)phenol with various aldehydes has been achieved using 10 mol% In(OTf)(3) and 30 mol% TsOH to produce the cis-fused hexahydropyrano[4,3-b]chromene derivatives in good yields, while the coupling of (E)-2-(5-hydroxypent-2-enyl)phenol with aldehydes under similar conditions affords the corresponding trans-fused hexahydropyrano[4,3-b]chromene derivatives.
Organic & Biomolecular Chemistry 07/2012; 10(32):6562-8. · 3.70 Impact Factor
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ABSTRACT: The present method demonstrates a rapid, effective and eco-friendly synthesis of palladium nanoparticles at room temperature using natural honey as a source of reducing and stabilizing agent. The functionally rich, honey, provides the necessary stabilizing and reducing properties for the encapsulation of highly stable Pd nanoparticles. Furthermore these honey derived Pd nanoparticles shows promising catalytic activity for the Suzuki reaction and hydrogenation of conjugated olefins.
Nanoscience and Nanotechnology Letters 04/2012; 4(4):420-425. · 0.53 Impact Factor
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ABSTRACT: Isatin reacts smoothly with indoles in the presence of a catalytic amount of molecular iodine under mild conditions to afford a novel class of di(indolyl)indolin-2-one derivatives in good yields. These molecules are found to possess a promising cytotoxicity against cancer cells only but not on normal cells.
Bioorganic & medicinal chemistry letters 02/2012; 22(7):2460-3. · 2.65 Impact Factor
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ABSTRACT: 1-Benzyl ethers of (E)- and (Z)-hex-3-en-1,6-diols and hept-3-en-1,7-diols undergo a smooth oxidative cyclization with DDQ in the presence of In(OTf)(3) through a sequential C-H bond activation and an intramolecular Prins cyclization to afford the corresponding trans- and cis-fused hexahydro-2H-furo[3,2-c]pyrans and octahydropyrano[4,3-b]pyrans respectively in good yields with an excellent stereoselectivity. Aryl tethered homoallylbenzyl ethers such as benzyl ethers of (E)- and (Z)-6-arylhex-3-enyl alcohols undergo a tandem Prins/Friedel-Crafts cyclization in the presence of stoichiometric amounts of DDQ and SnCl(4)via the benzylic C-H bond activation to furnish the corresponding trans- and cis-fused hexahydro-1H-benzo[f]isochromenes in good yields with complete stereoselectivity.
Organic & Biomolecular Chemistry 12/2011; 10(7):1349-58. · 3.70 Impact Factor
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ABSTRACT: Indole and its derivatives undergo smooth conjugate addition onto en-1,4-dione derived from isatin and acetophenone, in the presence of a catalytic amount of molecular iodine in acetonitrile under mild conditions to afford a novel class of 3-(1-(1H-indol-3-yl)-2-oxo-2-phenylethyl)indolin-2-one derivatives in good yields with high degree of 1,4-selectivity. Some of these compounds are found to exhibit modest antibacterial and antifungal properties.
Bioorganic & medicinal chemistry letters 08/2011; 21(21):6510-4. · 2.65 Impact Factor
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ABSTRACT: Biomolecules hosting the synthesis of nanoparticles has achieved considerable attention in recent decades due to their abundant availability, excellent biocompatibility and low toxicity. The present study demonstrates a rapid, cost-effective and eco-friendly fabrication of gold and silver nanoparticles at room temperature using natural honey as a source of stabilizing and reducing agent. The nanoparticles obtained were unambiguously characterized by using various characterization techniques such as transmission electron microscopy (TEM), UV-Visible absorption spectroscopy, X-ray diffraction and energy dispersive (EDX) X-ray analysis. The average size of Au and Ag nanoparticles are 10 and 12 nm respectively. Ag nanoparticles capped by honey exhibited superior antimicrobial activity while Au nanoparticles revealed passable activity against pathogenic bacteria and Candida albicans, including multi-resistant strains for the first time.
Journal of Nanoscience and Nanotechnology 08/2011; 11(8):6995-7000. · 1.56 Impact Factor
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ABSTRACT: An efficient and practical total synthesis of (+)-spirolaxine methyl ether is described. The phthalide-aldehyde 3 has been prepared via the Diels-Alder reaction between 1,4-unconjugated diene 5 and a long-chain acetylenic dienophile 6. The carbon framework of spiroketal sulfone 4 has been constructed from monobenzyl protected 1,5-pentanediol and the stereochemistry in both the phthalide portion and the spiroketal portion has been established by the Sharpless asymmetric epoxidation.
The Journal of Organic Chemistry 11/2010; 75(23):8307-10. · 4.45 Impact Factor
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ABSTRACT: Three-component coupling of aldehyde, indole and kojic acid has been achieved using a catalytic amount of InCl(3) under solvent free conditions to produce a novel series of 2-substituted aryl(indolyl)kojic acid derivatives in good yields and with high selectivity. These compounds are found to exhibit potent antifungal properties.
Bioorganic & medicinal chemistry letters 10/2010; 20(24):7507-11. · 2.65 Impact Factor
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Angewandte Chemie International Edition 08/2010; 49(34):5961-5. · 13.45 Impact Factor
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ABSTRACT: [Structure: see text] Under special conditions, N-phthaloyl-alpha-amino acid amides of 8-aminoquinoline can be either acetoxylated or arylated selectively at the beta-carbon. In certain cases, arylation can be effected at the gamma-carbon.
Organic Letters 08/2006; 8(15):3391-4. · 5.86 Impact Factor
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ABSTRACT: [reaction: see text] A useful process for the position-selective remote bromination of N-trifluoroacetyl-alpha-amino esters is illustrated for the isoleucine case. The 5-bromoisoleucine derivative shown above can be used for the synthesis of many modified amino acids, as described herein.
Organic Letters 07/2006; 8(13):2819-21. · 5.86 Impact Factor
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Organic Letters 07/2005; 7(13):2703-5. · 5.86 Impact Factor
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ABSTRACT: A short and highly stereocontrolled synthesis of the potent proteasome inhibitor 3 from the (S)-threonine-derived oxazoline 4 has been developed. The synthetic sequence is summarized in Scheme 1. Aldol coupling of the zinc enolate of 4 with isobutyraldehyde and subsequent silylation provided the TBS ether 5 diastereoselectively (10:1). Reductive cleavage of the oxazoline ring of 5 followed by Swern oxidation of the resulting amino alcohol afforded amino ketone 6, converted further by N-acylation to the acrylamide 7, whose structure was confirmed by X-ray crystallographic analysis. Acrylamide 7 was cyclized to 8 by a novel application of the Kulinkovich Ti(II)-cyclopentene complex. Silylation of 8 to 9 and radical cyclization at low temperature produced the bicyclic lactam 10 with complete control of all stereocenters. Hydroxy desilylation and N-deprotection of 10 gave the dihydroxy ester 11, which was converted to 3 by a novel three-step sequence: (1) demethylation with [Me2AlTeMe]2, (2) combined beta-lactonization and chlorination, and (3) desilylation to effect cleavage of the TBS ether.
Journal of the American Chemical Society 07/2005; 127(25):8974-6. · 9.91 Impact Factor
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ABSTRACT: [reaction: see text] A total synthesis of the salinosporamide analogue 3 is described that starts with the novel cyclization 4 --> 5.
Organic Letters 06/2005; 7(13):2699-701. · 5.86 Impact Factor
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ABSTRACT: Activated quinoline and isoquinoline undergo unexpected ring expansion by diazocarbonyl compounds via C-C insertion in the presence of 5 mol% of copper triflate to produce ethyl 1H-benzo[b]azepine-1-carboxylate and ethyl 3H-benzo[d]azepine-3-carboxylate, respectively, in excellent yields with a high degree of selectivity
Chemical Communications 10/2004; · 6.17 Impact Factor
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ABSTRACT: A rapid and efficient procedure is reported for the synthesis of nitriles by condensation of aldehydes with hydroxylamine hydrochloride in the presence of dibutyltin oxide supported on Al2O3 under microwave irradiation
Journal of Chemical Research 04/2001; 2001(5):190-191. · 0.04 Impact Factor
